A major national concern in the subsurface disposal of energy waste is the contamination of ground and surface waters by waste leachates containing toxic metals such as lead. There is a significant input of lead into terrestrial and aquatic ecosystems from solid waste disposal and from atmospheric deposition of anthropogenic pollutants. Lead is present in coal bottom and fly ash and is also released into the atmosphere from fossil-fuel combustion and from lead smelters. It is believed that lead is present as lead oxide (PbO) in the coal bottom and fly ash. Lead oxide is also released into the atmosphere from automobile emissions. Lead oxide is quite insoluble in water and its presence in terrestrial and aquatic systems poses a serious threat to the safety and ecology of these systems.
Microorganisms play a major role in the transformation of toxic metals present in wastes and affect their mobility in subsurface environments. Microbial activities affect dissolution, mobilization, and immobilization of toxic metals. Of particular concern is the microbial dissolution and remobilization of lead compounds in oxic and anoxic environments. Patterson [Marine Chemistry, 2, 69, 1984] observed the release of lead in seawater from the adsorbed to dissolved species after storage for three months. Bruland, et al. [Environ. Sci. Technol., 8, 425-432, 1974] noted that contaminated sediments released a greater fraction of their lead content under anaerobic conditions that did unpolluted sediments. Additionally troubling was the finding by Wong, et al. [Nature, 253, 263-264, 1975] that microorganisms in sediments from several Canadian lakes transformed certain inorganic and organic lead compounds into tetramethyl lead.
Applicants have now found that they can apply the role played by microorganisms in the biogeochemical and ecological cycles of lead in a positive fashion in order to solubilize toxic lead compounds. More particularly, applicants have found that an anaerobic bacterium which was isolated from coal beneficiation residue solubilizes a significant amount of lead oxide and an appreciable amount of lead sulfate. The solubilized metal, probably in the form Pb.sup.2+ associated as an organic complex, is then bioavailable to the microorganism, being found associated with the cell biomass. In addition, the solubilized metal is immobilized by a polymer-like substance produced by the microorganism.